This invention relates to a blank material for use as ceramic wiring substrates which can be used in the production of electronic components such as printed circuit boards. The invention relates also to a process for producing this blank material.
Ceramics have excellent thermal properties, electrical properties, and other properties, and therefore the development of wiring substrates utilizing ceramic bases has been and is being promoted. Processes for producing printed circuit boards (circuit substrates) by using ceramic bases include a process wherein an adhesive such as a cold-setting adhesive or a thermosetting adhesive is coated onto the side of a ceramic base such as boron nitride or the side of a copper foil having a specific pattern, and the ceramic base and the copper foil are registered at a specific position and then are bonded together by hot pressing or the like; another process wherein a copper foil is clad on a sheet of polyimide plastic with an adhesive, the copper-clad polyimide laminate is subjected to photoetching to form a conduit pattern, an adhesive is coated onto the side of the ceramic base or the side of the polyimide laminate, and then they are laminated; a further process wherein a concavity corresponding to a pattern is formed in a ceramic base, a copper foil adjusted into the form of a specific pattern is inserted into the concavity, and then they are directly bonded; and a still further process wherein a mixture (a paste) of a finely divided metallic powder such as Ag/Pd, Ag/Pt, Au, Pt or Cu, a glass frit and a vehicle is used to carry out screen printing to form a pattern on a ceramic base, and the patterned ceramic base is fired. Besides these processes, there are other processes such as that wherein a metallic layer is formed at the surface of a sintered ceramic base by a metallizing method to prepare a material for a ceramic wiring substrate, and then a conduit pattern is formed by a conventional etching method.
Still another process wherein a ceramic base and a copper foil are affixed with an adhesive to prepare a blank material for a ceramic wiring substrate, and a circuit board is produced by a conventional etching method has been proposed. According to this process, a ceramic circuit board having a fine circuit pattern can be easily produced. Further, it is unnecessary to use complicated steps, such as registration between the ceramic base and the circuit-patterned copper foil, which were necessary in the prior art. Furthermore, the process is inexpensive because expensive materials such as polyimide laminates are not used. However, inorganic and organic adhesives for obtaining good adhesion between the ceramic base and the copper foil have not been developed, and therefore the process described above has not been used.
An object of the present invention is to provide a blank material for use as a ceramic wiring substrate wherein a copper foil is caused to be strongly bonded to a ceramic base, and wherein a high density and fine pattern can be formed.
Another object of the present invention is to provide a process whereby the blank material for use as a ceramic wiring substrate can be produced on a mass production scale.